The EU's gas co-ordination group will meet in emergency session on Friday to consider shifting plentiful supplies of stored gas held by unscathed countries to those who are suffering from the ongoing dispute between Russia's Gazprom and Ukraine's state energy firm Naftogaz.

This emerged as the Czech premier, Mirek Topolánek, the current EU president, raised the "extreme option" of a three-way summit with Russia and Ukraine to resolve the growing political crisis.

These diplomatic moves came as Russian shipments of gas to the western Balkans, including Romania, Bulgaria, Macedonia, Greece and Turkey, shut down or were slashed by up to two-thirds. The disruption of supplies has also spread to Italy, Austria, Poland, Slovakia, Hungary and Slovenia, as Russia and Ukraine continued to blame each other for the commercial and political impasse.

The EU's gas co-ordination group comprises representatives from the 27 governments, commercial companies and transmission operators as well as European commission officials. Unusually, officials from both Gazprom and Naftogaz have also been invited to attend as the EU stepped up pressure on both to resolve their dispute.

The Czechs and commission today declared the situation "completely unacceptable" as supplies had been substantially cut "without warning and in clear contradiction with the reassurances given by the highest Russian and Ukrainian authorities". Commission officials indicated that the reassurances had been given by the Russian prime minister, Vladimir Putin, and his Ukrainian opposite number, Yulia Tymoshenko, as well as by top executives from both Gazprom and Naftogaz.

So far the commission has consistently labelled the dispute purely commercial and the EU demanded that gas supplies be restored immediately, with both Naftogaz and Gazprom resuming negotiations immediately.

But as the diplomatic crisis intensified, a top-level delegation of Czech and commission officials and ministers, which met the Ukrainian authorities in Kiev yesterday, flew to Berlin for talks with Gazprom executives later today.

Gazprom, though, claims that Ukraine is to blame for the disruption to suppliers. Its deputy chief executive, Alexander Medvedev, today accused the Ukrainians of unilaterally closing three export pipelines without warning - cutting supplies to one-seventh of previous levels.

He accused Ukraine of being in breach of its obligations as a transit country.

"It is unprecedented in the history of the gas market," he told a press conference in London. "Ukraine is in obvious breach of its obligations as a transit country. We are facing the challenge together with our European partners. We have become a hostage to irresponsible behaviour."

"We hope the situation will not continue for long. It is not just a question of a commercial risk but of technological risk as well."

Medvedev accused the Ukrainians of acting for political, not commercial, motives and demanded the return of gas which he alleged had been stolen.

Asked how long it would be before customers in western Europe would be affected by the row between Gazprom and the Ukraine, Medvedev said: "The situation is really very serious."

He said his company stood ready to negotiate at any time but that the Ukrainians were not at the negotiating table. "Why? You have to ask them," he said.

But the head of Naftogaz, Oleh Dubyna, told journalists in Kiev he would restart talks with Gazprom in Moscow on Thursday.